In a production line, in particular a processing line for foodstuffs, the properties of products are examined using X-ray techniques and the examination results can be used multiple times with regard to the further processing. For example, foreign bodies may be detected, and contaminated products may be removed from the food stream by sorting. Also, various properties of the foodstuff may be identified by X-ray examination. For example, fat layers can be measured, filling levels monitored, weights determined, or a count can be made.
It is also known to predetermine the correct cutting width of food slices and to control subsequent cutting tools in such a manner that the desired slice thickness or a desired weight is precisely cut off.
To increase the production throughput, as suggested in DE102005010183B1, modern cutting devices (so-called slicers) are capable of cutting more than just one food (for example, a bar). In the process, several foodstuffs are separated simultaneously (multiple lanes), that is, in parallel.
Moreover, in the X-ray examination used in medical technology, high-precision investigations are carried out by means of three-dimensional analyses. However, the techniques used are very expensive, and they are designed specifically for immobile objects.
On the other hand, in X-ray inspection in the industrial field, the desired solutions usually have to take up little space and they have to be cost effective in order to be able to examine products that move at high speed in a product stream. Here, the goal is to be easy on the X-ray tubes to increase their lifespan, and to achieve a high degree of X-ray safety, in spite of the fact that the products of the production stream are moving continually into a room that is protected from radiation, for example, by means of bulkheads, and again out of said room.
DE102005010183B1 describes how an X-ray inspection system determines measurement data for several food bars, and how this data is used for the individual advance control of each food bar as it moves toward the next slicer. Several food bars are here X-rayed simultaneously in slices by an X-ray radiation means.
Industrial production often involves a comprehensive production line having several different process work steps, into which the X-ray inspection unit has to be integrated, without substantially changing the existing processes. Therefore, the X-ray inspection unit has to be adapted to the existing processes, particularly to the transport speed of the product stream.
In industrial production, a product stream consisting of a plurality of successive products to be X-rayed one after the other commonly comprises several lanes or several partial streams. Such so-called parallel (multiple lane) product streams are usually characterized by mutually equidistant lateral spacings (viewed transversely to the transport direction). However, in X-ray inspection or radiography (including terahertz radiation) of such a parallel product streams, problems arise that considerably affect the validity of the results of the X-ray inspection in comparison to a single-lane product stream.
In the X-raying of parallel product streams, in which the products are conveyed next to one another in the conveyance direction (also referred to herein as the transport direction)—usually on a common conveyor belt—in a plurality of several, preferably equidistant, lanes that are next to one another, the following problem causes were primarily found.
In industrial X-ray inspection, inexpensive X-ray sources are used, for cost reasons, that are also of low intensity for reasons pertaining to occupational safety. Such X-ray sources are point-shaped radiation sources, which emit, by means of screening measures, a fan-like beam bundle (in the shape of a row in cross section) (the rest of the radiation can be shadowed, for example, by a slit). Due to the point-shaped radiation source, the radiation receiver (detector) (configured with one or several rows) can be of broader design than the product stream (see FIG. 1 for example, described further below).
As soon as the radiation path from the source to the detector is no longer vertical, but forms an angle with said (central) vertical row, the radiation path from the source to the detector increases according to this angle.
Depending on the width and the height of the products to be examined in the product stream, shadowing effects result between the products that are adjacent transversely to the product stream (along the detector row), preventing an unequivocal assignment of the image pixel generated at the time of the X-raying or the irradiation to the product, because the same X-ray beam passes equally through two laterally adjacent products (see FIG. 2). In the case of shadowing effects in a parallel product stream, an unequivocal assignment of the radiation image (gray value of the pixel) to a specific product or to the product lane is no longer possible. In the sense of the invention, X-ray inspection refers to X-raying or irradiation, wherein the term X-ray beams in this connection explicitly also includes terahertz beams.